__path__ (A Special Variable) in Python

In Python, special or “dunder” (double underscore) variables play a pivotal role in the internal workings of the language. These variables have special meanings and are used in various contexts. One such special variable is __path__.

What is __path__?

__path__ is a variable that is primarily defined for packages in Python. When a module is imported, Python sets a handful of these dunder variables; however, only packages get the __path__ attribute.

A package in Python is a way of organizing related modules into a single directory hierarchy. For example, if you have several modules that pertain to graphics operations, they can be grouped under a “graphics” package.

The __path__ attribute is used to determine the paths where the Python interpreter looks for modules inside the package. It’s a list that specifies the search path for sub-modules and sub-packages contained within the package.

Why is __path__ Important?

The primary significance of __path__ lies in its role in module lookup within packages. By manipulating this variable, one can alter the locations from which sub-modules of a package are imported. This offers flexibility in designing the structure of larger Python applications and frameworks.

An Example to Illustrate __path__

Let’s go through an example to understand the role of __path__.

Imagine you have the following directory structure:


my_package/
  |-- __init__.py
  |-- module1.py
  |-- module2.py

The directory my_package is a Python package because it contains an __init__.py file. When you import this package, Python automatically sets a few attributes for the package, one of which is __path__.

In a Python shell or script:


import my_package

print(my_package.__path__)

This might output something like:

Output:
['/path/to/directory/containing/my_package']

It shows the directory from which module1.py and module2.py will be imported when you do something like:


from my_package import module1

Modifying __path__

The power of __path__ comes from the fact that you can modify it. Suppose you have another directory named extra_modules containing some additional modules that you want to be part of my_package.

By appending this directory to __path__, you can seamlessly import modules from there as if they were part of my_package.

Here’s how you might modify the __path__ attribute in my_package/__init__.py:


import os

__path__.append(os.path.abspath('../extra_modules'))

Now, if extra_modules contains a module3.py, you can do:


from my_package import module3

Even though module3.py isn’t in the my_package directory, Python knows to look in extra_modules thanks to our modification of the __path__ variable.

Conclusion

In conclusion, the __path__ variable in Python provides a mechanism to guide the interpreter’s module search within packages. While you might not need to modify or interact with it in daily coding, understanding its purpose can be crucial when designing more complex Python projects or when debugging package imports.

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